Nest all namespaces

The compiler supports this now.  We can type less going forward.
No functional changes.

Signed-off-by: Stephan Pleines <pleines.stephan@gmail.com>
Change-Id: I29d6fa4f9aacc0e381f1a7637294db0392466995
diff --git a/motors/usb/cdc.cc b/motors/usb/cdc.cc
index e082156..5a668d8 100644
--- a/motors/usb/cdc.cc
+++ b/motors/usb/cdc.cc
@@ -19,8 +19,7 @@
     }                                        \
   } while (false)
 
-namespace frc971 {
-namespace teensy {
+namespace frc971::teensy {
 namespace {
 
 // Aka the Communications Device Class code, the Communications Class code,
@@ -428,5 +427,4 @@
   }
 }
 
-}  // namespace teensy
-}  // namespace frc971
+}  // namespace frc971::teensy